Generally speaking, offshore deposits of hydrocarbons require for their recovery the emplacement of a connection between the deposit and the surface installations that provide for transportation and storage of the fluids recovered. This connection is generally composed of wells equipped with submarine and/or aerial producing heads, and effluent or product piping between the producing heads and the separation and/or processing installations. These can be of very short length if the installations are located in proximity to the producing heads. The production installations make it possible to sort out the various phases of the product effluent, and provide a discharge means to a storage point for product(s) extracted from the deposit. The means described above are generally concentrated at least in part in one or more structures fixed to the sea bottom, or collected on the decks of floating structures.
Depending upon the flow, the nature of the product effluent, and the conditions of the outside environment, technological problems are frequently encountered that result in abandoning the development of a promising deposit discovery. Along these technological problems are the following examples:
(a) the inability to insure or maintain well product flow sufficient to the deposit profitably;
(b) the need to abandon the site prematurely while a substantial part of the product fluid remains in the deposit;
(c) the impossibility of insuring normal working conditions throughout the year due to adverse outside environments;
(d) finally, as soon as the depth of water becomes substantial and the environmental conditions severe, the existing technologies require installations of such size that they are reserved for working only large deposits. Those deposits so inconsistent that they may only be skimmed periodically are not worked. In any event, regulation of product flows and pressures, and the limitations of the latter imposed by the high level of safety required by confined installations combine to make them very complex. These installations require very skilled workers to operate and supervise them, even for deposits located in shallow water.
There are also deposits situated under a thin layer of "dead-terrain", in which the pressure is relatively low, regardless of the water depth. These pressure levels form a partial or complete bar to the present technology of development.
Certain deposits are also situated in zones where the surface of the sea is heavily traveled, or is partially obstructed by floating objects such as icebergs, iceflows, floatsum and driftwood. These deposits, sometimes associated with very bad conditions of visibility or detection, lead to a high probability of collision if all or part of the installation is located at the air-sea interface.